DNA chip technology is a technology for identifying a target expressed gene, by labeling the gene, hybridizing to DNA on a glass surface or silicon substrate, and observing the positions of immobilization. DNA chips make use of the spotting technique whereby cDNA or synthesized oligonucleotides are immobilized on a substrate, or the in situ (on chip) technique wherein oligonucleotides are directly synthesized on a substrate. A representative example of the latter is the “Gene Chip” of Affymetrix. In the spotting technique, DNA fragments of from several hundred to up to ten thousand types of genes can be arrayed within an area of several square centimeters on a substrate such as a glass slide, then subjected to an immobilization method using primarily electrostatic bonding and covalent bonding (Non-patent Document 1).
In immobilization by electrostatic bonding, a glass slide coated with polycations is spotted with DNA and oligonucleotides which are polyanions. The immobilization efficiency depends on their length. In order to observe a difference of one base in SNP analysis, it is necessary to use synthesized oligonucleotides of 20-30 bases, but if the lengths are short, it is difficult to achieve stable immobilization of DNA, and the efficiency decreases. Additionally, polyamines have been used for modification of the substrate surface of DNA chips, but they are coated on the entire solid phase, making detection of trace amounts of genes difficult due to non-specific adsorption of DNA (Non-patent Documents 2 and 3).
On the other hand, in the immobilization method using covalent bonding, a substrate is treated with a silane coupling agent having amino groups, aldehyde groups, epoxy groups, activated ester groups, vinyl groups, and the like, then bound to DNA to the ends of which amino groups, aldehyde groups, thiol groups, biotin and the like have been introduced. By this method, the stability of immobilized molecules is increased, but in cases where hybridization and the like are carried out, it is easily affected by the substrate surface, and in particular, there are reports that the first 20-30 bases from the surface are hardly used, so that problems of specificity and reproducibility arise quite easily. Recently, hybridization to synthesized oligomers covalently bonded to the surface under a liquid phase environment has become possible by arraying minute pieces of polyacrylamide gel on the glass surface, but a prior surface treatment process such as attachment of functional groups on the glass surface is unavoidable (Non-patent Document 4).
The search for drug discovery candidates and their target molecules efficiently by proteomics must depend on a direct and rational analysis based upon the ligand recognition ability of proteins. However, the DNA chips and protein chips available until now have the aforementioned drawbacks, and therefore do not have adequate performance for such analysis.    Non-patent Document 1: DNA Chip Ouyou Gijutsu (2000), Tadashi Matsunaga (ed.), Published by CMC Publishing Co., Ltd.    Non-patent Document 2: “DNA chip technology and its applications”, Protein, Nucleic Acids and Enzyme 43(13), (1998), Fusao Kimizuka, Ikunoshin Katoh, Published by Kyoritsu Shuppan CO., LTD, pp. 2004-2011.    Non-patent Document 3. Barrett J. C, Kawasaki E. S., “Microarrays: the use of oligonucleotides and cDNA for the analysis of gene expression”, Drug Discov Today, 8, 134-141, 2003.    Non-patent Document 4: Yershov G, Barsky V, Belgovskiy A, Kirillov E, Kreindlin E, Ivanov I, Parinov S, Cuschin D, Drobishev A, Dubilev S, Mirzabekov A., “DNA analysis and diagnostics on oligonucleotide microchips”, Proc. Natl. Acad. Sci. USA, 93, 4913-4918, 1996.